The initial circleci/*-browsers images was the intuitive first step in providing a convenient docker image with browsers preinstalled. In this image, the browser versions are static and does not provide the user with control over the browser’s version.
The new cimg/*-browsers images take a different direction and ship with Selenium preinstalled. Selenium is introduced as "an umbrella project for a range of tools and libraries that enable and support the automation of web browsers." Click here to read more.
You can compare the differences to the convenience images by looking at the publicly available template Dockerfile source:
Should I upgrade?
If you already have a test suite configured with the circleci/*-browsers images, upgrading to the new convenience image would be recommended if the project already has selenium as a dependency, or a switch to selenium is being made.
Installing Browsers and Browser drivers
Now that the new browser images do not provide the browsers preinstalled themselves, use the non-browser variant image (circleci or cimg namespaces), and implement the "browser tools" Orb into your configuration. This Orb provides the user the ability to choose which browser and versions they are testing on.
Another alternative would be to create build a docker image on top of the convenience image, and preinstall the browsers required for the project.